What formats do live forever?
I've had CDs degrade over time, in odd ways too... Sometimes the silver film peels away from the edges towards the center, and I've even had a few CDs succumb to something quite strange...
The silver data layer appears to have been "eaten away" by something, between the plastic and the coating protecting the data layer. It leaves fractal like trails and renders the CD unusable.
Both these have happened to CDRs as well as retail CDs. I'm at a loss to explain them, but short of making several copies and checking them periodically, what's the best format for lengevity?